Suggestions please, as ducted heat pump won't heat below +4C in Tasmania

We had an electric Daikin ducted system with MyAir and room sensors installed in March 2020 by one of Tassie’s biggest heating/cooling companies.

We’ve had a lot of problems with leaks, poor installation, design of outlets, etc. It’s been an absolute saga since day one!

We run it 24/7 through the colder months with a night cycle and a day cycle.

If the overnight is below +4 degrees C it takes forever to heat up when it switches over to the day cycle. In the beginning 5 hours to get from 18C (max overnight we are able to achieve) to 20C. Now 2 hours to achieve. It also struggles to heat up a bit extra in the evenings if the temp drops rapidly.

We have limitations on highest and lowest temp and two fan speeds - medium and high!

The installer service has been very positive but I can feel we are at the end of the road after 2 years, perhaps with one more run at Daikin who have also been helpful.

There is some question about the elements in the system the installer has put together and Daikin had some question about the MyAir which is actually designed for aircon, although works a heating system.

The installer has now told us in writing that no system installed in Tasmania will work in very cold weather!! I understand the process of how a heat pump works, but our system struggles below +4 degrees.

Basically what they have replaced a 25yo Fujitsu split system with doesn’t do the job and I’m wondering what our rights are from here or what else we could do.

I have the majority of our email correspondence as evidence. I have looked at the ACCC site.

Any input much appreciated.

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Welcome to the Community @MelCr28

It would be surprising if ‘no heat pump system in Tassie could handle +4C’. Not being an HVAC engineer, if your original requirement is documented and the system does not meet that requirement you could write a formal Letter of Complaint to the installing company citing your history and exactly what you want, eg a heating/cooling system that works in Tassie climate. While you may or may not ask for them to shoulder some or all costs (you did buy the system in good faith) you could ask for an engineered solution that will work for your needs. A booster might be the best solution, or a different technology heat pump.

You would be well served by including some statistics about other installations in your vicinity assuming you can document they work satisfactorily including comparisons to the buildings they are installed in.

As a point the words ‘struggles’ and ‘forever’ are subjective and I suspect you meant it once took 2 hours and now 5 to get up to 20C? edit: OP clarified the work done improved it from 5 hours to 2 hours.

This video is mostly about economics from a US group. A relevant image from it is

There are different heat pump technologies from the ‘standard’ that tapers off efficiency fairly ‘early’ regarding low temperatures. Note the need for a booster at lower temperatures. It seems like your Daikin may have a ‘standard’ heat pump and no booster?

Re the graph, for the example house the vertical axis is the required heating capacity, the horizontal the outside temperature. The insulation characteristics for this house in the US state of Minnesota (cold nasty winters) are in the video. Tassie does not get as cold in winter.

While not very informative, Daikin does make certain claims, this from Daikin EU.

Another long but instructive video is here. and includes this similar graphic to the above

Does it reinforce your system is running as it should, but not as you want or need? It may be a case of insufficient design and ‘grunt’? A secondary thought is how well insulated your ducting is?


Those people who live in northern Europe or Canada must all burn yak dung to keep warm as clearly no aircon will work at - 20c.


We’re actually talking below +4C, so that would cover WA, Vic, NSW and possibly even parts of Queensland!


Your point has been made. It appears there is something not right, but it could be the equipment, the installation, or the design, or a mix coupled with your house characteristics, eg insulation on the house and around the ducting.

Our winters are fairly benign and it is illogical a heat pump system, properly specified and engineered, would be inadequate when they work in other parts of the world, and perhaps even other parts of Australia :wink:

I have 2 Daikin splits rarely used for heating as I have a hydronic system, but they pumped out plenty of warmth on the occasion I needed them when it was around 2C and the hydronics were having a moment.

After watching one or both the videos and digesting the graphs of heat load vs capacity against temperature, is there anything you are focusing on beyond ‘it is not satisfactory’ and possibly getting worse? Note you have to consider that the differences between 2 hours and 5 hours is not just to raise your inside temp from 18 to 20, it is also dependent on the outside temps for the heat pump to work effectively, so including that in your observation is necessary.

Another thing to document is the air temperature coming out of the ducts against internal and outside temperatures to see if it seems to be working to its stated capacity.


Appreciate your response. Most of what you are talking about has been documented already by the installers. Their service has been great but they haven’t improved on the problem much, except it now only takes 2 hours to warm the house rather than 5 after repairing a range of leaks and tears in ducting and unit! We looked at hydronic but in our house structure there was no way to install neatly or easily and with no gas we are stuck with some version of what we have.


Yes. I am in NSW and I get winter mornings down to about -4c. My aircon does labour somewhat under those conditions, in part because it has to stop and de-ice from time to time.

The point is any heat pump loses efficiency as the ambient temperature becomes extreme. So as it gets very hot outside and you are trying to cool inside the outside heat exchanger becomes less effective trying to shed heat in hot air and the converse when trying to heat inside (and cool outside) when the ambient is very cold and it needs to gain heat from cold air.

As you cannot avoid thermodynamics you will either have to deal with it or pay for an over-built system that has extra capacity in adverse conditions. The vendors probably should tell you this before selling you a system.


‘Some version’ could be a second heat pump or a conventional electric booster added to the ducting, or add-on electric panels that only require a sparky. Not a recommendation just an example.

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I’ve attached a couple of links to Daikin’s technology for cold climates (typically consistently less than zero). There is as @PhilT has suggested a balance point at which ducted or heat pump based systems require boosting.

I’m not about to offer any expertise on that, other than to point to the content provided by Daikin on when boosting is required. The environments considered are typically all sub zero (IE less than 32F on the US imperial scale).

As a result of a combination of the performance of insulation of your home relative to installed heating capacity an upgrade may be required. The Daikin ‘expert’ installer should be able to say which is the greater concern. IE better insulated or greater heat pump capacity. If not it may be advisable to seek an appraisal from one of their competitors re an upgrade, or a professional insulation energy consultant.

Note: modern hydronics may operate best powered by a heat pump (air or ground sourced) rather than gas. It would seem unlikely your climate location and ducted system should need boosting. If it does, boosting can be by electrical or lpg (bottled) gas, which is only used in extreme conditions.

And from NZ which is at least as miserably cold if not more than Tasmania, mostly.

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Thanks Mark, that’s great info and we will have a look. The installers who customised our whole house ducted system are going back to the drawing board I think.

Someone has also given me the name of a company for a second opinion on the whole system.

We have good insulation so we do feel there is an issue with the components of the system. We ran a 5KW Fujitsu in the living area of our house prior to getting a whole house system and never had any problems regardless of outside temperature so we do have a comparison.


Does the ducting have adequate insulation? Most houses rely on ceiling insulation, ceiling grilles are holes in the insulation and if the ducting is not adequately insulated a lot of heat can be lost.

Norway reputedly has more heat pumps per capita than any other country. Most are air-air (cool the outside air to heat the inside air) so clearly some models work below 4°C.

Domestic heat pumps (A/C included) are a compromise, and are less efficient than theoretically achievable. It is worth comparing models to see if a larger up front spend yields a more efficient system. I haven’t seen comparisons of inverter models at various loads, theoretically a large system running at less than full capacity is more efficient than a smaller one that is flat out. Non inverter models are either running or not running so tend not to be more efficient at lower loads.

The following is an extract from a Daikin NZ brochure. The second linked web page In my prior post. A market closer to Tasmania in climate than the larger portion of Australia.

Note firstly for the particular models illustrated the outdoor temperature operating range of -15C to +16C. There are models not shown in the screen capture that will work down to -20C.

Actual thermodynamic performance is more complex as it needs to consider the relative humidity. Typically expressed as dry bulb and wet bulb temperatures. I’ve circled in red in the footnotes the conditions under which each unit achieves it’s rated output per Australian Standards. IE heating rated capacity in kWh is measured with an internal temp of 20C dry bulb and 15C wet bulb for an outdoor condition of 7C dry bulb and 6C wet bulb. 58% RH and 87% RH respectively, if I read the psychometric chart correctly.

As conditions move away from the conditions at which a unit is rated per the standard performance can decrease. As well as the outside ambient air temperature (dry bulb), the wet bulb (relative humidity) must also be known to consider any impact on performance.


mark_m Consumer Defender - are you agreeing or disagreeing with me? The reason I mentioned Norway is because people there are using heat pumps. To me that is a more convincing fact than a manufacturer’s brochure that says a piece of equipment will work at -15°C without saying how well.

Relative humidity isn’t very significant unless you are cooling humid air to phase transition (i.e. vapour to water or ice). The amount of vapour is small (maximum 2% @ 20°C) so the change of efficiency is down to the ratio of specific heats of water vapour to air (about 2:1) so the effect is 1%.or less.

[added] - the energy required for phase transition (e.g. condense water vapour to liquid) is more than a thousand times that needed to change the vapour’s temperature by 1°C. So most of the energy used to cool humid air is creating the condensation that goes down the drain. Once a house is cool and the excess water vapour is condensed, it takes far less energy to keep it at the desired temperature. As long as not too much air is exchanged with the outside bringing in more humidity.

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Definitely agree that heat pumps can be effective in cold and very cold climates. It’s important to note there are different systems (models) for different environments. Something that does need to be considered when,

Although the models typical of Norway, Sweden etc are not necessarily the same as marketed locally? Hence the prior reference from Daikin NZ’s products. Also evidence they can supply systems to suit Tasmania which has a similar range of climate. Daikin will have a psychometric performance chart in their design manuals which clarifies performance under different outdoor conditions, including allowance for defrost cycling. Likely in wet Tasmanian winters?

Note most manufacturers supplying the Aussie market recommend different models for outdoor environments where frosts are expected or colder. Compressor sump heaters being one.

The original post raised a concern their new system supplied was not performing as expected. Not to be taken as a general criticism of heat pump systems, it’s always frustrating when an expensive decision.

P.S. I’ve made a small addition to the topic title in case some see the discussion for anything more.

There is also valuable general topic discussion of other factors to consider for a ducted system install. How well heat pumps function in frost prone conditions might be a further discussion.


I have contacted other people locally (we’re on the north west coast of Tassie). One said their system (Mitsubishi) has never missed a beat, others (also Daikin) have had defrosting problems.

We had a clunky old Fujitsu room system before we had the ducted and that never missed a beat either. It sat in the same place as the new system, so not about environment. We also had a couple of mitsubishis in other rooms which worked fine. Sadly they got pulled out to make way for the ducted and I am now regretting it!

Am waiting to hear back from the installer as this system was put together from different elements (fan, unit, ducts, controller). We paid a lot of money for the system and I honestly cannot see why it doesn’t do what they say it should. Thanks to your feedback I am well armed, although a bit technically underqualified for some of your answers. If we get a solution I will come back and let you know.


Yes, please keep the community informed when appropriate. As an average consumer, none should need to argue the technical with the expert authorised supplier installer. It should suffice the consumer has an expected outcome providing it is stated clearly when requesting the quote to supply. The consumer is not likely competent to judge the capability or technical merits of the offer. By demonstration the supplied system either meets the agreed outcome or not. Fit for purpose can be a substantial point to make under ACL.

As a minimum outcome what performance would a reasonable consumer expect of a ducted system installed to meet heating needs of mid Winter NW Tasmania?


I agree and I thank you for all the reallly useful input. I do think “fit for purpose” is the key term here.

Minimum Performance; That it runs overnight at the temperature we set (which would only like be 19 or 20C) and works no matter the outside temperature, within reason.

We have a lot of cold nights and heavy frosts through June - August, so any system needs to be able to cope with that. Not many nights much below 0, and I understand the whole concept of how a heat pump functions, but if we could run at a higher temp overnight, mornings would not be an issue.

Certainly I would expect to be warm and not sitting with rugs on in the morning waiting for it to get to a reasonable temperature!!

Thanks again.


I guess this shows up the inadequacy of split systems as the temp gets up or down to quite high or low temps when it is really needed and probably applies to those very expensive heat pump hot water systems also. It seems there is no cost-effective substitute yet for gas heating that always works but the global warming experts are telling us it must be phased out. When it is cut off or banned I can see us going back to burning wood again in homely open fires or to power hydronic systems, unless electricity prices are capped as resistive heating is cost prohibitive.

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How so? The issue presented is a single under-performing ducted system. Heat pumps are used extensively in far colder continents than ours. Sometimes they are boosted by electric or gas in the extremes of their operational profiles.

Have you considered business as usual with any fossil fuel will contribute to climate change requiring more heat and more air conditioning more often, powered by what? Coal/wood fired a/c?

That is one way but the one that has traction is encouraging solar with batteries. Powering heat pumps with boosters works, and geothermal (ground) heat pumps while more expensive operate in a much wider range than the more common air-to-air variety most are familiar with.


Finally I have had a partially acceptable reply from the installers.

They are now admitting that our system may be underspecced (?) and are redesigning it.

They have suggested they split the house into 2 sections. The existing 18kw system would run the office, bedrooms, hall (which they estimate requires 10kw) and they would install another 10kw system to run the large living area (which they estimate requires 7.5kw).

Tassie electricity is hydro and we also have solar panels. The above makes a lot more sense and was an option we discussed at the outset but they decided on an 18kw system, the largest they could install without needing 3-phase in the fuse box (?).

So my question now is: will the area that only requires 10kw actually only use 10kw, for example, of the 18kw. Or will it use 18kw. I don’t understand all of this, so looking for a little more of your very expert input. I’m a bit concerned about the cost of running a 28kw system!!! Or will it only use what it needs to maintain the temperature.

I’m also assuming/hoping that with a bigger system it won’t struggle as much to achieve and maintain the temperature and may end up being more economical to run??

Thanks so much for your help to date. It’s been very useful.

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